High power electron discharge device



July 2, 1963 J. FEINSTEIN HIGH POWER ELECTRON DISCHARGE DEVICE 3 Sheets-Sheet 1 Filed March 21. 1960 .m R 8 all y 5 m m V 0 m n A m 6 e m J W Y B July 2, 1963 J. FEINSTEIN 3,096,462

HIGH POWER ELECTRON DISCHARGE DEVICE Filed March 21, 1960 3 Sheets-Sheet 2 0'; INVENTOR. Joseph Feinsrein LL Attorney i /KM July 2, 1963 J. FEINSTEIN HIGH POWER ELECTRON DISCHARGE DEVICE 3 Sheets-Sheet 3 Filed March 21, 1960 INVENTOR. Joseph Feinsfein BY 0 I,

M/flIW) Attorney United States Patent Ofi 3 ,096,462 Patented July 2, 1963 ice Jersey Filed Mar. 21, 1960, Ser. No. 16,313 32 Claims. (Cl. 315-3953) The present invention relates in general to electron discharge devices for generating high C.W. powers, and more particularly to a high power magnetron type device as of the coaxial, inside-out configuration.

In the past it has been d-ifiicult to achieve a high power, high frequency device of the magnetron type and obtain high eificiencies because of limited interaction area, the difficulties in suppressing undesired modes and the necessity for dissipating the large amount of unconverted (DC) power over a large enough area to reduce the power density to manageable proportions. Furthermore, previous structures have not provided cooling means at locations sutficiently close to the points of power dissipation to keep temperature gradients Within tolerable bounds. Other deficiencies in previous structures have existed in the means for starting the interaction in the electron discharge device and in acceptable means for attenuating reflected waves on the slow wave circuit of the devices.

The principal object of the present invention is to provide a high power microwave electron discharge device of the general coaxial, inside-out magnetron configuration.

One feature of the present invention is the provision of a novel electron discharge device wherein the electrons move in a direction orthogonal to the direction of wave propagation and interaction takes place between the wave and the electrons over a wave path length many wavelengths long.

Another feature of the present invention is the provision of a novel electron discharge device wherein the anode structure provides the desirable mode control and is aimendable to liquid cooling at locations sutficiently close to the points of power dissipation to keep temperature gradients Within tolerable bounds.

Another feature of the present invention is the probision of a novel electron discharge device of the magnetron nature wherein means are provided for dependable triggering of a cold cathode which is dependent upon the RF. wave field strength in the vicinity of the cathode for initiating emission.

Still another feature of the present invention is the I provision of a novel electron discharge device wherein the electrons move in a direction orthogonal to the direction of wave propagation with means provided on the cathode to attenuate reflected waves traveling on the RF. wave circuit.

Still another feature of the present invention is the provision of a novel electron discharge device provided with attenuation means for preventing operation of the device in undesired modes.

Other features and advantages of the present invention will become more apparent after a perusal of the following specification taken in conjunction with the ac companying drawings wherein:

FIG. 1 is a perspective view partially broken away, of a coaxial, inside-out magnetron configuration, electron discharge device embodiment of the present invention,

FIG. 2 is a horizontal cross-sectional view of the apparatus of FIG. 1 provided with a solenoid taken along the line 22 in the direction of the arrows,

FIG. 3 is a side cross-sectional view of the apparatus of FIG. 2 taken along line 33 in the direction of the arrows,

FIG. 3a is an enlarged view of that portion of the structure of FIG. 3 delineated by the line 3a3a,

FIG. 4 is an alternative embodiment of the anode structure shown in FIGS. 1-3,

FIG. 4a is still another alternative embodiment of the anode structure shown in FIGS. 1-3,

FIG. 5 is a perspective view of still another embodiment of the present invention showing a portion of the anode-cathode structure,

FIG. 6 is a perspective view of another alternative embodiment of the andoe structure,

FIG. 6a is a perspective view of still another alternative embodiment of the anode structure,

FlG. 7 is a fragmentary cross-sectional view of the anode-cathode structure showing another embodiment of the present invention,

FIG. 8 is an enlarged cross-sectional view of that portion of the structure shown in FIG. 7 delineated by line 8 8,

FIG. 9 is a fragmentary cross-sectional view of the anode-cathode structure showing still another embodh ment of the present invention,

FIG. 10 is an enlarged cross-sectional view of that portion of the apparatus shown in FIG. 9 delineated by line FIG. 11 is a longitudinal view of a linear embodiment of the apparatus of FIG. 10,

FIG. 12 is a perspective view of still another embodiment of the present invention illustrating a novel cathode structure,

FIG. 13 is a perspective view of the anode structure shown in FIGS. 1 and 2 illustrating the manner in which the synchronous electron stream and the RF. wave move around the anode structure, and

FIG. 14 is a perspective view of another embodiment of the present invention illustrating a novel cathode structure.

Referring now to FIGS. l-3a, the coaxial, inside-out magnetron comprises a thick-walled, hollow cylindrical anode 21 which forms, with its inside surface, a circular electric mode waveguide 22, as for example, a TE guide. A hollow. cylindrical cathode 23 as, for example, a cold cathode of beryllium copper whose emission is initiated by the electric fields of the R.F. wave in the device sur rounds and is spaced from the anode 21. The cathode 23 and the anode 21 are vacuum sealed to one another at their ends by means of a pair of annular insulating flange members 24 as of ceramic.

The anode structure 21 is %4 A thick in a radial direction, where A is the cut-off wavelength of the waveguide 22, and is provided with a plurality of spaced-apart, elongated resonator slots 25 connecting the wave-electron interaction space between the anode structure 21 and the cathode 23 with the waveguide 22. These resonator slots 25 subdivide the anode structure 21 into a plurality of anode members 26 which are all joined at their two extremities. The outer surface of each anode member 26 is provided with a slot resonator 27 M4 deep extending the length thereof.

Each anode member 26 is also provided with a pinrality of tubular fluid passages 28 extending the entire length thereof for passing a cooling fluid through each anode member to dissipate the heat generated in the anode structure 21. Annular cooling fluid manifolds 29 are vacuum sealed to each end of the anode structure 21 surrounding the ends of all the passages 28 thereby conmeeting all the fluid passages 28 together. An inlet 30 is provided in one manifold 29 and an outlet 30 is provided in the other whereby a cooling fluid can be passed through the manifolds and through the passages 28 in the anode structure 21.

For operation of the device as an amplifier an input wave permeable window 31 as of ceramic is vacuum sealed within the opening at one end of the anode structure 21. A standard circular waveguide 32 projects outwardly from around the window 31 and is provided on the end thereof with a standard waveguide flange 33 for connection to other microwave apparatus. The smaller end of an outwardly flared hollow waveguide 34 is vacuum sealed in the opening in the anode structure opposite the input window 31. An output wave permeable window 35 is vacuum sealed within the outward end of the flared waveguide 34, and a standard waveguide flange 36 on the end of the flared waveguide 34 provides means for coupling the waveguide 34 to other microwave elements.

A solenoid 37 surrounds the electron discharge device for providing an axially directed magnetic field in the interaction space between the anode structure 21 and the cathode 23. Conventional means (not shown) are provided for maintaining the cathode 23 at a negative potential with respect to the anode structure 21 for pro viding the electric held between the anode structure 21 and the cathode 23 necessary for crossed-field interaction.

When the novel electron discharge device illustrated herein is operating as an amplifier, an electromagnetic wave in the circular electric mode is propagated through the input window 31 and into the hollow waveguide 22. The circumferential electrical currents associated with this mode on the inner surface of the anode excite the /4?\ slot resonators 25 and produce high electric fields at the open ends of the slot resonators 25 23. By capacitive coupling, the adjacent M4 slot resonators 27 are excited in opposite phase to form the desired 'rr mode in the interaction space between the anode structure 21 and the cathode 23. These resultant electric fields adjacent the cathode serve to initiate the emission from the cold cathode 23. Magnetron type interaction then takes place in the space between the cathode and the anode, and energy is transferred from the electrons to the wave propagating in the waveguide 22 uniformly along both the axial length and the circumference of the structure via the resonator slots 25 communicating with the waveguide 22. The slotted region of the anode structure is many guide wavelengths long, preferably at least ten but always greater than one wavelength, and the structure can be lengthened if higher powers are desired in a single tube.

Since the anode members 26 are /M thick in a radial direction and the slot resonators 27 are only /4 deep, each anode member 26 is provided with a large solid portion /ztt in length which is amenable to liquid cooling by means of the fluid passages 28. A cooling fluid, for example, water is passed through the cooling fluid manifolds 29 and thence through the fluid passages 28 to cool the large solid portions of the anode members 26 where the majority of unconverted DC. power is dissipated.

As can be seen from the above, the anode structure with the AA slots 25 and the AA slots 27 makes possible the desired 1r mode operation within the magnetron interaction region between the anode 21 and the cathode 23 and the desired Zero mode operation in the waveguide 31 while allowing liquid cooling of the anode. Other combinations of electrical slot lengths can be employed while providing mean for fluid cooling by maintaining the difference in resonator slot length as an 11 multiple of M2 where n can have any positive integer value such as, for example, 0, 1, 2, 3, etc.

Unlike conventional traveling wave interaction, the electrons synchronous velocity is at right angles to the direction of propagation of the wave, i.e. the total wave velocity vector. The electron spokes of space charge will then lie along helical contours with a pitch of one resonator per waveguide half wavelength, as shown in FIG. 13 and as will be explained in more detail below.

The outwardly flared hollow waveguide 34 provides a larger cross-sectional area for the guide in the vicinity adjacent the cathode U of the output window 35 thereby allowing the window 35 to pass greater powers and avoiding high attenuation and possible arcing since the power density is reduced.

Whereas the present invention has been illustrated as an amplifier, it could also be embodied as an oscillator. The waveguide would be closed off at its ends by reflecting end lates to provide a cavity resonator with an iris opening for extracting the oscillatory energy. A thermionic emitter would be provided to act as a priming source for the oscillator.

Also, the device shown in FIGS. l-3a can be operated as an oscillator by feeding a portion of the output back to the input. The oscillation frequency would be controlled by altering the total phase shift around the loop.

Referring now to FIGS. 4 and 4a there are shnow alternative embodiments of th eanode structure of P10 S. l-3a. In these alternative embodiments all the slot resonators are coupled to the TE mode waveguide 22 while still obtaining the 7r mode in the interaction space between the cathode 23 and the anode structure 21 and still providing a thick anode structure to permit liquid cooling of this anode. Since the phase reversal is required between adja cent slots to maintain the 1r mode interaction, all slots are provided to communicate with the circular electric waveguide 22 and adjacent slots differ in length by an odd multiple of M2. According to the embodiment shown in FIG. 4 each Ax length of a 117i slot resonator 38 is foreshortened by loading the capacitive and inductive portions of the slot resonator so that it occupies the same length as the adjacent %7\ slot resonator 25. Alternatively, as shown in FIG. 4a the effective length of a M4 slot resonator 39 may be retained by reducing the inductive portion (slot width) compared to the capacitive section while each )\/4 slot resonator 39 still communicates with the electric mode guide 22 and is separated from the next M4 slot resonator 39 by a /4?\ slot resonator 25.

Referring now to FIGS. 5, 6, and 6a there are shown mode control means for damping out undesired modes. As shown in FIG. 5 dielectric members 41 such as ceramic or glass rods or tubes are positioned within the device at the opening of the slot resonators 25 into the waveguide 22 where voltage nulls occur for the desired mode. These elements 41 can be carbonized to provide doss for undesired modes. At very high power levels where heat cannot be dissipated easily, a lossy fluid such as water can be passed through tubular elements 41 to provide absorptive means which will damp out undesired modes and which can be cooled by circulation outside the vacuum envelope of the electron tube. in such a case where the lossy fluid in the tubes 41 serves as both absorptive means and cooling means for the anode structure, the fluid passages 28 will not be necessary. Thus, the open end and closed end slot resonators 25 and 27' respectively can be the same electrical length as, for example, M4 as shown in FIG. 5 and thus the electrical length corresponds to an ":0 positive integer multiple of M2 difference in electrical length of the adiacent slots as mentioned above.

As shown in FIG. 6 circular or helical grooves 42 approximately A/4 deep can be cut in the inside walls of the anode 43. The interior of these grooves are then filled with lossy material, such as Kanthal, and these grooves will then effectively damp out axial modes in the Waveguide 22.

An alternative damping means shown in FIG. 6a comprises thin walled damping rings 41) of lossy material as carbonized ceramic positioned in shallow circular grooves (alt/4) in the interior surface of the anode structure 21". These damping rings pass across the resonator slots 25" which open into the central waveguide thereby providing damping both for slot modes which have high electric fields at this point and for non-circular electric waveguide modes. A multiplicity of such damping rings 40 can be randomly positioned along the axial height of the anode structure to insure effective mode control.

Referring now to FIGS. 7-12 there are shown means for enhancing the initiation of emission from a cold cathode which is dependent upon the RP. field strength in the vicinity of the cathode for initiation of its emission.

As shown in H05. 7 and 8 a number of resonant slots 44 are cut into the surface of the cathode 45 to act as parasitic elements enhancing the RF. field at the cathode. This group of slots can be positioned anywhere about the cylindrical cathode in the present circularly symmetrical device but would be employed primarily in the input region of a linear device or of a cylindrical device which has a radial input instead of the axial input shown with the present device. The use of these slots 44 enables a larger anode-cathode separation to be employed, thereby leading to higher efiiciency and greater mode stability.

Instead of a group of resonant slots the cathode 46 (see FIGS. 9 and in a cross-field device can he provided with grooves therein forming an identical slow wave circuit 4-7 as the slow wave circuit 48 provided on the anode structure 49. Also, in a linear crossed-field electron discharge device under certain circumstances, as when the ends of the circuit are uncoupled (see FIG. 11), the RF. wave can be applied directly to the cathode 51 when a slow wave circuit 52 is provided thereon. When an RF. wave is applied to the slow wave circuit 52 by an RF. input means 53, cold cathode emission is initiated and gives rise to electron emission which leads to fields at an anode 54 provided with a similar slow wave circuit 55. Power is then extracted from the anode 54 by an output means 56. Internal terminations 57 as, for example, absorbing means are provided at the end of the cathode and anode slow Wave circuits 52 and 55 op posite the input and output means 53 and 56, respectively. By terminating both input and output structures internally, the stability problem is solved. For the forward traveling wave power flows on the anode in only one direction because of phase cancellation in the reverse direction. Since the input signal will be attenuated as it moves down the cathode structure 51, the termination 57 may not be necessary on the cathode 51, but this termination will provide protection against reflections.

Referring now to H6. 12 there is shown a further embodiment of the present invention for controlling the operation of the device described here. A plurality of strip cathodes 59 as of the thermionic emission type are positioned in axially aligned grooves in the cold cathode 50 and are radially set back from the surface of the cathode 50. During low power operation of the device when there is insuilicient RF. field to operate the cold cathode, the strip cathodes 50 afford control of the current entering the interaction space.

As can be seen in EEG. 13, because of the finite guide wavelength Ag there is a twist to the electron spokes of space charge with a pitch of one resonator for each waveguide half wavelength. The direction of this twist depends on the direction of wave propagation in the guide. For this reason, and because the space charge is highly nonlinear at high power levels, there will be no gain for a wave traveling in the opposite direction in the guide (i.e. a reflection}. it is even possible to provide attenuation for reflections without disturbing the forward propagating Wave to any great extent.

Referring now to FIG. 14 helical grooves 58 approximately V4 deep can be cut in the inside surface of the hollow cylindrical cathode 59. The direction in which these grooves spiral is selected to be opposite in direction to the spiral of the helical contours of the electron spokes synchronous velocity and the RF. Wave. These grooves will therefore attenuate reflected waves traveling on the anode since the helical configuration of these reflected waves conforms to the configuration of grooves 58 in the cathode 59. The configuration of the grooves 58 will not substantially disturb the helical propagation of electrons synchronous with the forward of RF. waves on the anode since those waves are progressing in a hellcal path oppositely directed to the path of the grooves 58.

The crossed-field amplifier as described above is designed to produce OW. output powers on the order of a megawatt at the X frequency band and with efficiencies on the order of 60%.

Since many changes could be made in the above structure and many further embodiments of the invention produced without deviating from the scope of the invention, the foregoing specification and drawings are to be taken as purely illustrative and not in a limiting sense.

What is claimed is:

I. An electron discharge device using crossed electric and magnetic fields for the wave-electron stream interaction therein comprising, in combination, a hollow circular anode structure, the inner surface of which defines a circular electric mode waveguide; a hollow circular cathode surrounding and spaced from the outer surface of said anode structure to form the wave-electron interaction space therebetween, said cathode having an emis sion surface facing said anode structure; and means at opposing ends of said anode structure for propagating electromagnetic energy into and out of said waveguide defined by said anode structure, said anode structure having a plurality of radial resonator slots formed therein and providing communication between the circular electric mode waveguide and the interaction space between said cathode and anode and said resonator slots communicating with said circular electric mode waveguide over a length of said guide exceeding one wavelength of the dominant circular electric mode propagating in said guide.

2. The electron discharge device of claim 1 wherein the exterior surface of said anode structure is provided with at least one radial resonator slot between the ad jacent resonator slots that communicate with the circular electric mode Waveguide, the effective electrical lengths of the resonator slots which communicate with the circular electric mode waveguide and the resonator slots in the exterior surface of said anode structure differing by Int/2 where A is the cutoff wavelength of the structure and n is a positive integer.

3. The electron discharge device of claim 2 wherein the resonator slots alternate in electrical length between AA and .4x around the anode structure.

4. The electron discharge device of claim 1 wherein adjacent resonator slots differ in electrical length by rill/2 where is the cutoff wavelength of the structure and n is a positive odd integer.

5. The electron discharge device of claim 1 including cooling passages longitudinally within said anode structure.

6. The electron discharge device of claim 1 wherein said anode structure is provided with electromagnetic wave absorptive means positioned at the radial inward portion of the resonator slots in said anode structure whereby undesired modes of operation of the device are damped out by said absorptive means.

7. The electron discharge device of claim 6 wherein said absorptive means includes hollow tubes positioned longitudinally of said anode structure at the radial inward portion of said resonator slots and means for circulating a lossy fluid through said hollow tubes.

8. The electron discharge device of claim 1 including circular ridges on the inside surface of said anode structure defining grooves therebetween and absorptive means positioned within said grooves, whereby undesired modes with axial currents in said circular electric mode waveguide are attenuated.

9. The electron discharge device of claim 8 wherein said absorptive means includes lossy material positioned within said grooves and extending across said resonator slots in said anode structure whereby undesired slot modes and waveguide modes are attenuated.

10. The electron discharge device of claim 1 wherein said cathode is a cold cathode and is provided with resonant slots in the inside surface thereof to facilitate the initiation of emission therefrom.

11. The electron discharge device of claim 1 characten ized further in that said cathode is a cold cathode and is provided with a slow wave circuit on the interior surface thereof corresponding to the slow wave circuit of said anode thereby to aid in initiating emission from said cathode.

12. The electron discharge device of claim 1 wherein said cathode is provided with helical grooves with a lead directed oppositely to the direction of the lead of the R.F. space charge wave traveling adjacent to said anode whereby reflected waves on said anode are attenuated by means of said grooves.

13. The electron discharge device of claim 1 wherein said means for propagating electromagnetic energy out of the guide defined by the inner wall of said anode comprises an outwardly flared hollow waveguide projecting from one end of said anode structure excited for propagating the dominant circular electric mode and an electromagnetic wave permeable window vacuum sealed in the largest end of said outwardly flared waveguide.

14. An electron discharge device using crossed electric and magnetic fields (for the wave-electron stream interaction therein comprising, in combination, an anode structure provided with a slow wave circuit and a cathode spaced from said anode and having an activated surface facing said slow wave circuit, said cathode being provided with a resonant structure whereby said resonant structure on said cathode and said slow wave circuit on said anode cooperate to enhance the interaction between the electron stream and the electromagnetic wave traveling in the device.

15. The electron discharge device of claim 14 wherein the resonant structure on said cathode is a slow Wave circuit similar to the slow wave circuit on said anode and including means for introducing onto the cathode the wave to be amplified by the device.

16. An electron discharge device using crossed electric and magnetic fields for the wave-electron stream interaction therein comprising, in combination, a hollow circular anode structure, the inner surface of which surrounds a circular space, a hollow circular cathode surrounding and spaced from the outer surface of said anode structure to form the wave-electron interaction space therebetween, said. cathode having an emission surface facing said anode structure, said anode having a plurality of radial resonator slots formed therein, the effective electrical length of adjacent resonator slots differing by ilk/2 Where A is the cutoff wavelength of the structure and n is a positive integer and at least every other resonator slot extending entirely through said anode structure providing communication between the circular space surrounded by said anode structure and the interaction space between said cathode and said anode structure and said resonator slots communicating with said circular space defined by said hollow circular anode structure over a length of said space exceeding one wavelength of the dominant circular electric mode propagating in said space.

17. The electron discharge device of claim 16 including cooling passages longitudinally of said anode structure for carrying a fluid which will cool said anode structure.

18. The electron discharge device of claim 16 wherein said anode structure is provided with electromagnetic wave absorptive means positioned longitudinally of said anode structure at the radial inward portion of those resonator slots extending entirely through said anode structure whereby undesired modes of operation of the device are damped out by said absorptive means.

19. The electron discharge device of claim 16 including circular ridges on the inside surface of said anode structure defining grooves therebetween and absorptive means positioned within said grooves, whereby undesired modes with axial currents in the walls of said anode structure surrounding the circular space are attenuated.

20. The electron discharge device of claim 16 wherein 8 only alternate resonator slots communicate with the circular space and are of an effective electrical length of m and the remainder of said resonator slots are of an effective electrical length of AA.

21. The electron discharge device of claim 16 including means at opposing ends of said anode structure for propagating electromagnetic energy into and out of the circular space defined by said anode structure whereby electromagnetic waves propagating through the electron discharge device will be amplified.

22. An electron discharge device using crossed electric and magnetic fields for the wave-electron stream interaction therein comprising, in combination, a hollow circular anode structure, the inner surface of which surrounds a circular space, a hollow circular cathode surrounding and spaced from the outer surface of said anode structure to form the wave-electron interaction space therebetween, said cathode having an emission surface facing said anode structure, said anode structure having a plurality of radial resonator slots formed therein and providing communication between the circular space and the interaction space between said cathode and anode structure and electromagnetic wave absorptive means positioned at the radial inward portion of the resonator slots of said anode structure whereby undesired modes of operation of device are damped out by said absorptive means.

23. Electron discharge device of claim 22 wherein the exterior surface of said anode structure is provided with at least one radial resonator slot between the adjacent resonator slots that communicate with the circular space, the effective electrical length of the resonator slots which communicate with the circular space and the resonator slots in the exterior surface of said anode structure differing by Ila/2 where 7\ is the cut off wavelength of the structure and n is a positive integer.

24. Electron discharge device of claim 22 including circular ridges on the inside surface of the anode structure defining grooves therebetween and absorptive means positioned within said grooves, whereby undesired modes with axial currents in the walls of said anode structure surrounding the circular space are attenuated.

25. The electron discharge device of claim 22 including means at opposing ends of said anode structure for propagating electromagnetic wave energy into and out of the circular space defined by said anode structure whereby electromagnetic waves propagating through the electron discharge device will be amplified.

26. The electron discharge device of claim 25 including means for feeding back a portion of the output from the electron discharge device to the input whereby the electron discharge device will operate as an oscillator.

27. An electron discharge device including a cold cathode provided with resonant slots in the emitting surface thereof to facilitate the initiation of emission therefrom.

28. An electron discharge device including an anode provided with a slow Wave circuit and a cold cathode provided with a slow wave circuit on the emitting surface thereof corresponding to the slow wave circuit of said anode thereby to aid in initiating emission from said cathode.

29. An electron discharge device using crossed electric and magnetic fields for wave-electron stream interaction comprising, in combination:

(a) an anode structure;

(b) a cathode structure spaced from said anode structure to form a wave-electron stream interaction region spaced therebetween; and

(0) means for producing an electron stream in said wave-electron stream interaction region;

(1) said anode structure adapted for propagating an electromagnetic wave and in which the total wave velocity vector at all points on the anode structure is in a direction substantially orthogonal to the mean direction of said electron 9 stream and travels over a length of said interaction region longer than a wavelength of the dominant mode propagated by said anode structure;

(2) said cathode, said anode and said means for producing said electron stream adapted to produce cumulative interaction between said electron stream and said electromagnetic wave in said wave-electron stream interaction region and transfer energy from said electron stream to said traveling electromagnetic wave propagated by said anode over the length of said anode structure.

30. The electron discharge device according to claim 29 wherein said anode is provided with circumferential alternating symmetry for propagating an electromagnetic wave in said interaction region with a phase velocity substantially equal to and in substantially the same direction as the velocity of said electron stream.

31. An electron discharge device using crossed electric and magnetic fields for wave-electron stream interaction comprising, in combination:

(a) an anode structure;

(12) a cathode structure spaced from said anode structure to form at least one wave-electron stream interaction region spaced therebetween; and

() means for producing at least one electron stream in said wave-electron stream interaction region;

(1) said anode structure adapted for propagating an electromagnetic wave and in which the total wave velocity vector at all points on the anode structure is in a direction substantially orthogonal to the mean direction of said electron stream and travels over the length of said anode structure longer than a wavelength of the dominant mode propagated by said anode structure;

(2) said anode provided with circumferential alternating symmetry for propagating an electromagnetic wave in said interaction region with a phase velocity substantially equal to and in sub- 10 stantially the same direction as the velocity of said electron stream;

(3) said cathode, said anode and said means for producing said electron stream adapted to produce cumulative interaction between said electron stream and said electromagnetic wave in said wave-electron stream interaction region over the length of said anode structure to transfer energy from said electrode stream to said traveling electro-magnetic wave.

32. An electron discharge device of claim 31 wherein (a) said anode structure and said cathode structure are of substantially cylindrical shape and coaxial, (b) said electron stream forms a twist the length of said anode structure, and (c) said cathode is provided with grooves in the surface thereof,

(1) said grooves having a twist,

(2) the pitch of said grooves in said cathode being reversed with respect to the pitch of said twist of said electron stream and corresponding to the pattern of cathode currents associated with undesired electromagnetic waves traveling in said interaction region adjacent said cathode whereby said grooves on said cathode interrupt the cathode current associated with said undesired electromagnetic waves to attenuate said undesired electromagnetic waves.

References Cited in the file of this patent UNITED STATES PATENTS 2,678,407 Brown et al May 11, 1954 2,815,469 Sixsmith Dec. 3, 1957 2,824,998 Molnar Feb. 25, 1958 2,832,005 Brown Apr. 22, 1958 2,930,932 Geiger Mar. 29, 1960 FOREIGN PATENTS 7,869 Japan Sept. 6, 1958 

1. AN ELECTRON DISCHARGE DEVICE USING CROSSED ELECTRIC AND MAGNETIC FIELDS FOR THE WAVE-ELECTRON STREAM INTERACTION THEREIN COMPRISING IN COMBINATION, A HOLLOW CIRCULAR ANODE STRUCTURE, THE INNER SURFACE OF WHICH DEFINES A CIRCULAR ELECTRIC MODE WAVEGUIDE; A HOLLOW CIRCULAR CATHODE SURROUNDING AND SPACED FROM THE OUTER SURFACE OF SAID ANODE STRUCTURE TO FORM THE WAVE-ELECTRON INTERACTION SPACE THEREBETWEEN, SAID CATHODE HAVING AN EMISSION SURFACE FACING SAID ANODE STRUCTURE; AND MEANS AT OPPOSING ENDS OF SAID ANODE STRUCTURE FOR PROPAGATING ELECTROMAGNETIC ENERGY INTO AND OUT OF SAID WAVEGUIDE DEFINED BY SAID ANODE STRUCTURE, SAID ANODE STRUCTURE HAVING A PLURALITY OF RADIAL RESONATOR SLOTS FORMED THEREIN AND PROVIDING COMMUNICATION BETWEEN THE CIRCULAR ELECTRIC MODE WAVEGUIDE AND THE INTERACTION SPACE BETWEEN SAID CATHODE AND ANODE AND SAID RESONATOR SLOTS COMMUNICATING WITH SAID CIRCULAR ELECTRIC MODE WAVEGUIDE OVER A LENGTH OF SAID GUIDE EXCEEDING ONE WAVELENGTH OF THE DOMINANT CIRCULAR ELECTRIC MODE PROPAGATING IN SAID GUIDE. 